Manufacture of dichlorethane



ug 29, 1944. J. A. s. HAMMOND MANUFACTURE OF DICHLORETHANE Filed May 24,1943 Patented Aug. 29, 1944 MANUFACTURE F DICHLORETHANE Jolm A. S.Hammond, Glenbrook, Conn., assignor to U. S. Industrial Chemicals, Inc.,New York, N. Y., a corporation of Delaware Application May 24, 1943,Serial No. 488,141

3 Claims.

This invention relates to the production and purification ofdichlorethane or, as it is frequently designated in the trade, ethylenedichloride. Dichlorethane has been prepared heretofore by reactingethylene and chlorine within a body of liquid dichlorethane. The productof the reaction, after treatment with an aqueous alkali to neutralizeany acid present, has been separated into layers, one aqueous and theother containing dichlorethane and water. Upon distillation of thedichlorethane, the first fraction containing the water has beenseparated and the remainder recovered as anhydrous dichlorethane ofcommerce.

This commercial dichlorethane contains certain impurities in minuteproportions. The exact nature of the impurities is not known, but theirpresence renders the product unstable during storage and shipment andunsuitable for certain uses for example in the manufacture of some typesof synthetic rubber.

It is the object of the invention to provide an improved method ofpurifying crude dichlorethane whereby the impurities mentioned areeliminated and a stable product is obtained.

Other objects and advantages of the invention will be apparent as it isbetter understood by reference to the following specification and theaccompanying drawing, which illustrates diagrammatically an apparatussuitable for the practice of the method.

have discovered that the impurities present in crude dichlorethane canbe removed therefrom in two steps, in the rst of which only materialboiling below 71.5 C. (the boiling point of the azeotrope ofdichlorethane and water) is separated as vapor. The second step consistsof distillation with water so regulated that only the azeotrope ofdichlorethane and water is withdrawn as vapor. The azeotrope iscondensed and wet dichlorethane is separated. The wet dichlorethane canbe dried by another distillation to eliminate the water or alternativelyby contact with a desiccating material. Evidently'the impurities areeliminated in the vapor and water phases respectively of the first andsecond distillation, since these impurities do not occur in the nalproduct.

In the practice of the invention, I prefer to follow the procedure of myco-pending application Ser. No. 486,993 filed May 14, 1943, in whichsmall amounts of anhydrous ferric chloride, i, e. from approximately0.05% to 0.25% by weight of the liquid dichlorethane, are added Whilethe ethylene and chlorine are reacting in a body of liquiddichlorethane. The ferric chloride in the relatively minute quantitiesused acts as a depressant for the substitution reaction, and thusprevents to a large extent the formation of higher chlorinated productssuch as trichlorethane. By this means I am able to limit the reaction toone of addition, as follows:

One of the major impurities in commercial dichlorethane is thuseliminated.

Referring to the drawing, 5 indicates a reactoi consisting of a suitablereceptacle provided preferably with heads 6 and I and tubes extendingtherethrough to permit circulation of cooling water introduced through apipe 9 and Withdrawn through a pipe I0. Ethylene and chlorine,preferably in the molecular proportions of 1.1:1 are introduced throughpipes II and I2 and are delivered by a pipe I3 to the reactor 5 which issubstantially lled with a body of liquid dichlorethane. The liquidoverflows through a pipe I4 to a separator I5. A part of the liquid iswithdrawn through a pipe I6 and returned to the reactor 5 by a pump Iland pipe I8. Vapors from the separator I5 are withdrawn through a pipeI9 and delivered to a scrubbing tower 20. Water may be introduced at thetop of the scrubbing tower through a pipe 2|- to recover from the vaporshydrochloric acid which may be present. The solution escapes through apipe 22. The undissolved vapors are delivered through the vent 23.Anhydrous ferric chloride, preferably in the form of an alcoholsolution, is delivered in the required proportions from a receptacle 24through a pipe 25 controlled by a valve 26 to the reactor 5. Since aportion of the dichlorethane is withdrawn continuously, ferric chloridemust be added similarly to maintain the required proportion in thereactor 5.

A portion of the dichlorethane is withdrawn from the separator I5through a pipe 2l and is delivered to a neutralizer 28 preferablyprovided with an agitator 29. An aqueous solution of an alkali such assodium hydroxide is introduced through a pipe 29 in the proportionsnecessary to neutralize any acid present and also to decompose the smallamount of ferric chloride which remains in the dichlorethane. Thedlchlorethane overflows to a compartment 30 and is delivered by a pump3| and pipe 32 to the middle portion of a column 33 provided with platesor trays 34. The bottom of the column is heated by steam passing througha coil 35. A condenser 3l is provided at the top of the column and iscooled by water circulating through the pipes 38 and 39 to maintain atemperature below '11.5 C., for example approximately 70 C.. Thecondenser prevents vapors consisting of the azeotrope of d1- chlorethaneand water from escaping while low boiling material which may be presentis Withdrawn as vapor through a pipe 40 and discharged.

The mixture of dichlorethane and water is withdrawn through a pipe 4|and enters the middle portion-of another distillation column 42 havingplates or trays 43. The column is heated by the introduction of steamthrough a pipe 44. Water is fed to the top of the column through a pipe45. The to'p of the column is provided with a condenser 46 which ismaintained by circulation of water-through pipes 41 and 48 at atemperature of '11.5 C., thus permitting withdrawal of the azeotrope ofdiethylene chloride and water as vapor at the top of the column througha pipe 49. Suillcient water is introduced through the pipe 45 to ensurethe withdrawal of all of the dichlorethane, and water and impurities arewithdrawn through a pipe 50 at the bottom of the column.

The vapor, consisting of the azeotrope of dichlorethane and water, isdelivered by the pipe 49 to a condenser 5| through which water iscirculated by pipes 52 and 53. The condensed azeotrope is delivered by apipe 5'4 to a separator 55 provided with a vent 56. In the separator thecondensate settles in` two layers, the upper of which is principallywater which is Withdrawn through a pipe 51 and returned to the upperpart of the column 42. The lower layer, consisting of wet dichlorethane,escapes through a pipe 58 to a column 59 having plates or trays 60. Thecolumn is heated at the bottom by steam introduced through a coil 6|.The column is provided with a condenser 63 maintained, by circulation ofwater through pipes 64 and 65, at a temperature of '11.5 C. Theazeotrope of diethylene chloride and water is separated as vapor whichescapes through a pipe 66, and dry dichlorethane is withdrawn through apipe 61 at the bottom of the column. 'Ihe azeotrope is delivered to acondenser 68 cooled by water circulated throughthe pipes 69 and 10. Thecondensate is withdrawn through a pipe 1I and delivered to a separator12 having a vent 13. The upper water layer is discharged through a pipe14. The lower layer, consisting of wet dichlorethane, is withdrawnthrough a pipe 15 and delivered to the upper part of the column 59. Thecolumn is so operated as to continuously deliver dry dichlorethane atthe bottom, and the product is free from the impurities mentioned andconsequently stable in storage and shipment.-

In place of the column 59, and the distillation conducted therein, I mayutilize a similar column which may be tllled with pieces of a suitabledesiccating agent such as sodium or potassium hydroxide. In that event,the condenser 68 and the separator 12, with their pipe connections, areeliminated. The wet dichlorethane percolates upward through thedesiccating agent, which removes water therefrom. Dry dichlorethane iswithdrawn at the top of the column and is free from the impuritiesmentioned. It is a stable product which may be stored and shipped. It issuitable for purposes for which the dichlorethane of commerce, as nowavailable, cannot be utilized.

Various changes may be made in the procedure and in the apparatusemployed without departing from the invention or sacricing theadvantages thereof.

I claim:

1. The method of purifying crude dichlorethane which comprisesneutralizing the acid therein, heating the dichlorethane to vaporize andremove material having a boiling point below 71.5 C., distilling thedichlorethane with sulcient water to vaporize and separate all of thedichlorethane as the azeotrope of dichlorethane and water boiling at'71.5 C., condensing the azeotrope vapor, separating the condensate intoa watery layer and a layer consisting of wet dichlorethane, and removingthe water from the wet dichlorethane. l

2. The method of purifying crude dichlorethane which comprisesneutralizing the acid therein, heating the dichlorethane to vaporize andremove material having a boiling point below 71.5 C., distilling thedichlorethane with sufficient water to vaporize and separate all of thedichlorethane as the azeotrope of dichlorethane and water boiling at'11.5 C., condensing the azeotrope vapor, separating the condensate intoa watery layer and a layer consisting of wet dichlorethane, and againdistilling the wet dichlorethane to remove the water and dichlorethaneas the azeotrope leaving a residue of dry dichlorethane.

3. The method of purifying crude dichlorethane which comprisesneutralizingthe acid therein, heating the dichlorethane to yvaporize andremove material having a boiling point below 71.5 C., distilling thedichlorethane with sufficient water to vaporize and separate all of thedichlorethane as the azeotrope of dichlorethane and water boiling at71.5 C., condensing the azeotrope vapor, separating the condensate intoa watery layer and a layer consisting of wet dichlorethane, anddehydrating the wet dichlorethane by contact with a solid alkali metalhydroxide. l

JOHN A. S. HAMMOND.

